UNIVERSITY  OF  CALIFORNIA  PPBLICATION8 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


THE  ECONOMICAL  IRRIGATION  OF 

ALFALFA  IN  SACRAMENTO 

VALLEY 

BY 

S.   H.  BECKETT  and  R.   D.   ROBERTSON 


(Based  on  work  done  under  co-operative  agreement  between  the  Office  of 
Public  Roads  and  Rural  Engineering  and  the  State  Engineering  Department  of 
California  and  between  the  Office  of  Public  Roads  and  Rural  Engineering  and  the 
University  of  California   Agricultural   Experiment   Station.) 


BULLETIN  No.  280 

May,  1917 


UNIVERSITY   OF  CALIFORNIA   PRESS 

BERKELEY 

1917 


Benjamin  Ide  Wheeler,  President  of  the  University. 

EXPERIMENT  STATION  STAFF 

HEADS   OF   DIVISIONS 

Thomas  Forsyth  Hunt,  Director. 

Edward  J.  Wickson,  Horticulture    (Emeritus). 

Herbert  J.  Webber,  Director  Citrus  Experiment  Station;   Plant  Breeding. 

Hubert  E.  Van  Norman,  Vice-Director;  Dairy  Management. 

William   A.   Setchell,  Botany. 

Myer  E.  Jaffa,  Nutrition. 

Robert  H.  Loughridge,  Soil  Chemistry  and  Physics   (Emeritus). 

Charles  W.  Woodworth,  Entomology. 

Ralph  E.  Smith,  Plant  Pathology. 

J.  Eliot  Coit,  Citriculture. 

John  W.  Gilmore,  Agronomy. 

Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 

Frederic  T.  Bioletti,  Viticulture  and  Enology. 

Warren  T.  Clarke,  Agricultural  Extension. 

John  S.  Burd,  Agricultural  Chemistry. 

Charles  B.  Lipman,  Soil  Chemistry  and  Bacteriology. 

Clarence  M.  Haring,  Veterinary  Science  and  Bacteriology. 

Ernest  B.  Babcock,  Genetics. 

Gordon  H.  True,  Animal  Husbandry. 

James  T.  Barrett,  Plant  Pathology. 

Fritz  W.  Woll,  Animal  Nutrition. 
*A.  V.  Stubenrauch,  Pomology. 

Walter  Mulford,  Forestry. 

W.  P.  Kelley,  Agricultural  Chemistry. 

H.  J.  Quayle,  Entomology. 

Elwood  Mead,  Rural  Institutions. 

J.  B.  Davidson,  Agricultural  Engineering. 

H.  S.  Reed,  Plant  Physiology. 

D.  T.  Mason,  Forestry. 

William  G.  Hummel,  Agricultural  Education. 

John  E.  Dougherty,  Poultry  Husbandry. 

S.  S.  Rogers,  Olericulture. 
fFRANK  Adams,  Irrigation  Investigations. 

H.  S.  Baird,  Dairy  Industry. 

David  N.  Morgan,  Assistant  to  the  Director. 

Mrs.  D.  L.  Bunnell,  Librarian. 

IRRIGATION  INVESTIGATIONS 

(In  cooperation  with  Office  of  Public  Roads  and  Rural  Engineering,  U.  S.  Depart- 
ment of  Agriculture,  and  State  Engineering  Department  of  California) 

Frank  Adams  S.  H.  Beckett 

H.  A.  Wads  worth 
Samuel  Fortier,  Chief  of  Irrigation  Investigations,  Office  of  Public  Roads  and 

Rural  Engineering. 
W.  F.  McClure,  State  Engineer  of  California. 


*  Died  February  12,  1917. 

t  In  co-operation  with  office   of  Public   Roads  and  Rural   Engineering,   U.    S. 
Department  of  Agriculture. 


THE  ECONOMICAL  IRRIGATION  OF  ALFALFA 
IN  SACRAMENTO  VALLEY1 

BY 
S.  H.  BECKETT  AND  E.  D.  ROBERTSON 


SUMMARY 

PRACTICAL   SUGGESTIONS   FOR   SACRAMENTO   VALLEY 

ALFALFA  GROWERS 

For  Medium  Loams 
1.  Depth  of  irrigation  water  required  per  annum  to  produce  the  best  yield  of 

alfalfa  from  medium  loam  soils  in  Sacramento  Valley  

30  to  36  inches,  depending  on  rainfall 

'  2.  Desirable  depth  of  irrigation  water  to  apply  to  alfalfa  on  medium  loam  soils 
at  each  irrigation  6  to  9  inches,  depending  on  depth  of  soil 

3.  Usual  number  of  irrigations  per  season  for  alfalfa  on  medium  loam  soils  in 

Sacramento  Valley  where  water  supply  is  sufficient 3  to  5 

4.  Desirable  size  of  border  or  strip  checks  for  alfalfa  on  medium  loam  soils  

30  to  50  feet  wide  by  300  to  600  feet  long,  depending  on  grade  and  soil 

5.  Desirable  grades  for  border  checks  on  medium  loam  soils  

3  to  6  inches  per  100  feet 

6.  Size  of  irrigating  ' '  head ' '  most  common  for  alfalfa  on  medium  loam  soils 

in  border  checks  of  this  size  in  Sacramento  Valley  

2  to  10  cubic  feet  per  second  per  check 

For  Very  Gravelly  or  Sandy  Soils 

7.  Depth  of  irrigation  water  required  per  annum  with  careful  practice  for  alfalfa 

on  very  gravelly  and  sandy  soils  in  Sacramento  Valley  48  to  60  inches 

8.  Desirable  depths  of  irrigation  water  to  apply  to  alfalfa  on  very  gravelly  and 

sandy  soils  at  each  irrigation  3  to  4  inches 

9.  Desirable  number  of  irrigations  for  alfalfa  on  very  gravelly  soils  in  Sacra- 

mento Valley  2  to  3  per  cutting 

10.  Desirable  size  of  rectangular  checks  for  alfalfa  on  very  gravelly  or  sandy 

soils  in  Sacramento  Valley  100  feet  by  100  feet 

11.  Desirable  size  of  irrigating  "head''  for  alfalfa  on  very  gravelly  soils  in 

checks  of  this  size  5  to  6  cubic  feet  per  second  per  check 

For  Heavy  Soils 

12.  Depths  of  irrigation  water  required  per  annum  for  alfalfa  on  ll heavy"  soils 

in  Sacramento  Valley  (clays  and  clay  loams)  30  to  36  inches 

13.  Desirable  depth  of  irrigation  water  to  apply  to  alfalfa  on  heavy  soils  at  each 

irrigation  2  to  4  inches 

14.  Desirable  number  of  irrigations  for  alfalfa  on  heavy  soils  in   Sacramento 

Valley  2  to  3  per  cutting 

15.  Desirable  size  of  border  or  strip  checks  for  alfalfa  on  heavy  soils  

30  to  50  feet  wide  by  300  to  600  feet  long,  depending  on  grade  and  soil 

16.  Desirable  grades  for  border  checks  on  heavy  soils  1  to  3  inches  per  100  feet 

17.  Desirable  size  of  irrigating  "head"  for  alfalfa  on  heavy   soils  in  border 

checks  of  this  size  1  to  4  cubic  feet  per  second 

1  This  bulletin  presents  a  brief  resume  and  summary  of  a  more  complete 
report  of  the  investigations  discussed,  prepared  under  the  joint  authorship  of 


274  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

INTRODUCTION 

From  two  and  one-half  to  three  acre-feet  of  irrigation  water  per 
acre  per  year  is  sufficient  for  the  growth  of  maximum  economic  yields 
of  alfalfa  on  the  medium  loam  soils  of  Sacramento  Valley.  This  is  the 
conclusion  drawn  from  experiments  covering  a  six-year  period  at  the 
University  Farm  at  Davis,  and  of  observations  during  one  to  two  years 
on  fifty-four  Sacramento  Valley  alfalfa  farms. 

In  addition  to  the  particular  studies  from  which  the  above  con- 
clusion is  drawn,  these  experiments  and  observations  have  been  con- 
cerned with  the  duty  of  water  for  alfalfa  on  botli  the  lighter  and  the 
heavier  soils  of  the  valley,  the  quantities  of  water  it  is  desirable  to 
apply  to  Sacramento  Valley  alfalfa  fields  at  single  irrigations,  desirable 
irrigation  ' '  heads ' 7  for  Sacramento  Valley  alfalfa  fields,  the  percentage 
of  moisture  in  the  soil  necessary  to  prevent  wilting,  and  the  amount 
of  moisture  above  the  wilting  percentage  that  produces  the  most 
satisfactory  growth. 

EXPERIMENTS  AT  THE  UNIVERSITY  FARM  AT  DAVIS 

The  duty-of-water  experiments  conducted  at  Davis  covered  the 
period  1910  to  1915,  inclusive.  During  1910  and  1911,  8.19  acres  in 
square  and  contour  checks,  each  0.20  to  1  acre  and  averaging  0.28 
acre  in  area,  were  utilized.  From  1912  to  1915  the  work  was  confined 
to  3.48  acres  divided  into  15  square  checks  averaging  0.23  acre  each. 
The  soil  of  these  plats  is  classed  by  the  Bureau  of  Soils  and  the 
University  of  California  Agricultural  Experiment  Station  as  Yolo 
loam.2 

In  addition  to  check  plats  which  were  not  irrigated,  the  various 
annual  depths  of  water  applied  were  12,  24,  36,  and  48  inches,  for  the 
full  six  years  of  the  experiment,  with  additional  plats  receiving  annual 


Frank  Adams,  Ralph  D.  Robertson,  S.  H.  Beckett,  Wells  A.  Hutchins,  and  O.  W. 
Israelsen,  printed  in  the  fifth  biennial  report  of  the  California  State  Department 
of  Engineering,  and  reprinted  as  Bulletin  No.  3  of  that  department.  The  investi- 
gations were  made  as  a  part  of  the  co-operative  irrigation  investigations  in  Cali- 
fornia conducted  under  agreement  between  the  Office  of  Public  Roads  and  Rural 
Engineering  (prior  to  July  1,  1915,  the  Office  of  Experiment  Stations)  of  the 
United  States  Department  of  Agriculture,  the  State  Department  of  Engineering 
of  California,  and  the  California  Agricultural  Experiment  Station.  The  work 
at  the  University  Farm  at  Davis  has  been  under  the  local  supervision  of  Professor 
S.  H.  Beckett,  assisted  by  O.  W.  Israelsen  and  Roy  Wray.  The  work  on  Sacra- 
mento Valley  alfalfa  farms  and  on  the  temporary  experimental  plat  at  Willows 
was  done  under  the  immediate  supervision  of  Ralph  D.  Robertson,  assisted 
chiefly  by  Wells  A.  Hutchins.  Soil  moisture  studies  were  largely  made  by  O.  W. 
Israelsen. 

2  U.   S.  Dept.   of  Agr.,  Bureau  of   Soils,   Reconnoissance   Soil   Survey   of  the 
Sacramento  Valley,  California. 


IRRIGATION    OF    ALFALFA    IN    SACRAMENTO    VALLEY  275 

depths  of  18  inches  and  60  inches  during  the  last  four  years  of  the 
experiment. 

The  total  depths  of  30,  36,  48,  and  60  inches  were  given  in  indi- 
vidual applications  of  7.5  inches,  9  inches,  12  inches,  and  15  inches, 
respectively.  In  1910,  1912,  and  1913,  following  winters  of  low  rain- 
fall, the  first  irrigations  were  given  immediately  after  the  first  cuttings, 
but  in  1911,  1914,  and  1915,  following  relatively  wet  winters,  irrigation 
began  after  the  second  cutting. 

All  of  the  plats  were  large  enough  to  represent  normal  field 
practice,  so  the  work  should  be  classed  as  field  experiments  rather 
than  laboratory  experiments.  Irrigation  water  was  supplied  from  a 
pumping  plant  on  the  tract  delivering  approximately  0.9  cubic  foot 
per  second. 

Throughout  the  experiments  the  practice  followed  was  to  irrigate 
just  as  soon  as  possible  after  removing  the  crop  from  the  field.  Be- 
cause of  the  small  irrigating  head  available,  slip-joint  pipe  was  used 
on  the  larger  checks  to  aid  in  even  distribution. 

In  the  time  of  cutting,  raking,  shocking,  and  hauling  the  hay 
standard  field  practices  always  were  observed.  That  is  to  say,  the 
alfalfa  usually  was  cut  when  one-tenth  to  one-third  in  bloom  and  the 
hay  generally  was  raked  the  same  day,  shocked  the  following  day,  and 
hauled  as  soon  as  it  was  dry  enough  to  be  stacked  without  heating, 
never  being  left  until  the  leaves  were  dry  enough  to  fall  off  when 
handled.  The  curing  and  removal  of  the  hay  from  the  field  required 
from  five  to  seven  days. 

The  following  table  summarizes  the  results  of  these  experiments 
at  Davis  over  the  full  six-year  period,  including  the  average  cost  of 
production  and  the  average  profit  per  acre : 

TABLE  NO.  1 

Summary  of  Alfalfa  Duty-of-Water  Investigations  at  Davis,  1910-1915 


CO 

O  o 

CB  cS 

to  " 
SI  0 

••*  'u 

u 

u 

•si 

s* 

Yield, 

tons  per  acre 

A 

<v 

Q)     t>     £H 

3  c3  S 

>  ?  * 

UJG&- 
^  ^  .^ 

8-2 

o 
u 

a>  u 
^  u 

0>   Jj 

1910 

1911 

1912 

1913 

1914 

1915 

Average 

3ft 

None 

3.85 

5.94 

5.52 

2.75 

2.89 

2.35 

3.88 

$27.16 

$8.73 

$18.43 

2 

6 

12 

4.78 

7.52 

6.51 

4.31 

5.83 

4.84 

5.63 

39.41 

15.37 

24.04 

3 

6 

18 

7.02 

5.69 

8.02 

6.46 

6.80 

47.60 

19.35 

28.25 

4 

6 

24 

6!6o 

8^38 

8.32 

6.89 

9.96 

7.96 

7.92 

55.44 

23.22 

32.22 

4 

71 
'2 

30 

7.53 

9.54 

9.43 

7.97 

11.06 

8.32 

8.98 

62.86 

26.45 

36.41 

4 

9 

36 

7.58 

9.33 

9.38 

8.22 

12.48 

8.63 

9.27 

64.89 

27.96 

36.93 

4 

12 

48 

8.45 

9.52 

8.63 

8.83 

10.62 

8.05 

9.02 

63.14 

29.10 

34.04 

4 

15 

60 

10.17 

7.25 

10.70 

5.55 

8.42 

58.94 

29.44 

29.50 

Market  val 

ue  of  hay, 

1910, 

1911,  and  1912, 

$11  per  ton;  1913,  $9;  1914,  $4; 

1915,  $8. 

2  Labo 
Water  figi 

r  of  production,   inclui 
ured  at  $1.70  per  acre 

ling  cutting,   raking,  shock 
-foot.     Labor  for  irrigation 

ing,  and  hauling,  figured  at  $2.25  per  ton. 
figured  at  50  cents  per  acre  per  irrigation. 

276 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Examination  of  this  summary  indicates  that  while  both  the  average 
maximum  yields  and  the  average  maximum  profits  were  greatest  in 
the  case  of  annual  applications  of  36  acre-inches  of  irrigation  water 
per  acre,  neither  the  average  increase  in  yield  nor  the  average  increase 
in  profits,  with  applications  at  the  rate  of  36  acre-inches  per  acre  per 
year,  over  the  average  yields  and  profits  with  applications  at  the  rate 


DEPTH  OF  IRRIGATION  IN  INCHES 


12 


16 


Z4 


30 


36" 


43 


60 


ii 


I  II  ■  II  II  I 

m  ii  n  ii  ii  i 


i  ii 


n  ii  i 
ii  ii  i 


■  ■ 

ii  ii  i 

ii  ii 

ii  1 1 

ii  1 1 


Fig.  1. — Diagram  showing  results  of  alfalfa  duty  of  water  experiments  at 
University  Farm,  Davis,  1910  to  1915.  Note  the  maximum  yield  with  an  annual 
application  of  36  inches  of  water.  The  most  economical  yields  were  obtained  with 
annual  applications  of  30  to  36  inches. 

of  30  acre-inches  per  acre  per  year,  was  large  enough  to  be  material, 
with  water  costing  at  the  rate  figured  in  the  Davis  experiments.  It  is 
plain,  however,  that  to  the  extent  that  water  costs  less  than  $1.70  per 
acre-foot  the  increase  in  net  profits  with  annual  depth  of  36  inches 
over  the  figures  for  annual  depths  of  30  inches  would  be  correspond- 
ingly greater,  and  very  much  greater  if  water  were  paid  for  at  the 


IRRIGATION   OF    ALFALFA    IN    SACRAMENTO   VALLEY  277 

flat  annual  rate  of  $1.50  or  $2  per  acre,  as  was  the  case  in  a  number 
of  the  Sacramento  Valley  areas  included  in  the  general  investigation. 
The  significant  fact  about  the  results  at  Davis  is  that  the  increase 
in  yield  tends  to  become  negligible  above  annual  depths  of  30  to  36 
inches,  indicating  that  under  conditions  at  Davis,  or  similar  thereto, 
a  maximum  allowance  of  36  acre-inches  per  acre  per  year  is  ample. 
This  is  further  brought  out  graphically  in  the  accompanying  chart 

(fig.D. 

The  most  marked  change  from  year  to  year  in  the  relation  of  the 
averages  to  each  other  took  place  in  the  60-inch  applications.  The 
1912  yield  from  the  most  heavily  irrigated  plat  was  more  than  10  tons 
per  acre,  but  the  average  dropped  to  8.42  tons  per  acre  by  1915,  and 
had  the  investigations  been  conducted  longer  this  average  doubtless 
would  have  decreased  each  year.  The  1915  yield  was  only  5.55  tons 
per  acre,  owing  to  the  quantity  of  rank  water  grass  which  had  sup- 
planted the  alfalfa. 

A  wide  variation  in  the  seasonal  rainfall  and  in  the  length  of  the 
growing  season  was  observed  at  Davis.  Both  of  these  factors  seemed 
to  have  a  decided  effect  on  the  yields  of  hay,  as  shown  by  the  following 
table : 


TABLE  NO.  2 

Eelation 

of  Climate  to  Yields  of 

Hay  at  Davis 

Season 

Rainfall 

Length  of  growing 

A 

Dates 

season1 

Number 
of  days 

Average 
temper- 
ature, 
o  F 

Number 

of 
cuttings 

Average 
yield  of  hay 
per  acre 
from  all 
checks 

1909-1910 

11.90 

Mar.  22-Oct.  10 

202 

57.7 

6 

6.36 

1910-1911 

23.18 

Feb.  27-Oct.  7 

222 

58.3 

6 

8.37 

1911-1912 

9.46 

Mar.  3-Oct.  10 

221 

57.9 

6 

8.12 

1912-1913 

8.74 

Mar.  4-Sept.  17 

197 

58.0 

5 

6.49 

1913-1914 

28.70 

Feb.  6-Oct.  26 

262 

60.0 

6 

8.94 

1914-1915 

20.05 

Jan.  23-Oct.  13 

263 

59.5 

6 

6.52 

Average 

17.00 

Feb.  23-Oct.  9 

228 

58.6 

7.48 

1  Period  between  date  of  last  killing  frost  in  the  spring  and  the  date  of  cutting  last  crop  the 
following  fall. 

Immediately  following  the  harvesting  of  the  last  crop  at  Davis,  on 
October  13,  1915,  five  areas,  each  containing  100  square  feet,  were  laid 
off  on  each  plat  included  in  the  experiment  and  the  number  of  plants 
in  each  area  counted.  The  probable  number  of  plants  per  acre  was 
figured  from  the  average  of  these  counts.  By  field  count  a  good 
stand  of  mature  alfalfa  was  found  to  contain  an  average  of  one  and 
one-half  plants  per  square  foot.  With  this  as  a  basis  of  comparison, 
the  following  table  was  compiled : 


278  UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION 


TABLE  NO.  3 

/ENT  OF 

Alfalfa  Stand  Remaining  at  I 

Six- Year  Experimental  Period 

Number 
of  plats 

17,30 

Depth 

of  water 

applied, 

in. 

Number 
of  plants 
per  acre 

8,625 

Per  cent 
of  good 
stand  re- 
maining 

13.2 

18,29 

12 

22,216 

34.0 

19,28 

18 

30,928 

47.3 

20,27 

24 

33,977 

52.0 

21,26 

30 

41,382 

63.3 

22,25 

36 

39,422 

60.3 

23,24 

48 

38,333 

58.7 

31 

60 

17,598 

26.9 

This  shows  the  effects  of  the  two  extremes  in  the  application  of 
water,  especially  when  it  is  remembered  that  the  observations  on  the 
60-inch  application  extended  over  a  period  of  only  four  years,  and  in 
this  time  the  stand,  as  a  result  of  over-irrigation,  was  reduced  to  an 
estimated  average  of  only  27  per  cent  of  the  original. 

INVESTIGATIONS  ON  SACRAMENTO  VALLEY  ALFALFA  FARMS 

In  selecting  the  areas  away  from  Davis  to  be  included  in  the  wider 
investigation  care  was  taken  to  include  enough  fields  so  that  there 
would  be  represented  the  major  soil  types  of  the  valley,  as  determined 
by  the  soil  surveys  of  the  Bureau  of  Soils  and  of  the  University  of 
California  Experiment  Station,  whose  soil  classifications  have  been 
followed  in  this  report;  also  to  give  the  investigations  as  wide  a 
geographical  distribution  as  possible,  so  that  the  differences  in  rainfall 
could  be  taken  into  consideration.  Accordingly,  during  the  irrigation 
seasons  of  1913  and  1914,  between  40  and  50  representative  farms  were 
under  observation  in  the  neighborhood  of  Gridley,  Los  Molinos,  Orland, 
Willows,  Woodland,  and  Dixon,  this  work  being  supplemented  in  1915 
by  detailed  studies  on  a  single  ten-acre  tract  five  miles  northeast  of 
Willows,  and  by  general  observations  and  measurements  on  four  other 
farms. 

In  every  case  where  the  amount  of  water  used  was  measured  the 
crop  yields  were  ascertained  by  the  most  satisfactory  means  available. 
In  some  cases  crops  either  were  sold  in  bulk  according  to  scale  weights 
or  baled,  making  exact  weights  available.  In  a  few  cases  stacks  were 
measured  or  a  sufficient  number  of  shocks  to  be  representative  of  the 
whole  were  hauled  to  nearby  scales  and  the  average  weight  per  shock 
obtained.  In  a  large  number  of  cases  the  average  weight  of  shocks 
was  ascertained  by  weighing  on  the  ground. 


IRRIGATION    OF    ALFALFA    IN    SACRAMENTO    VALLEY 


279 


Table  No.  4  below  summarizes  the  results  of  the  measurements  on 
Sacramento  Valley  farms  during  1913  and  1914. 


TABLE  NO.  4 

Summary  of  Results  of  Alfalfa  Duty-of- Water  Measurements  on  Fifty-four 
Farms  in  Sacramento  Valley,  1913  and  1914 


Name  of  area 

Average 

rainfall, 

in. 

Number 
of  fields 
included 

covered 
by  obser- 
vations 

Gridley 

22.241 

14 

284.22 

Los  Molinos 

26.112 

12 

130.40 

Orland 

19.23 

7 

214.52 

Willows 

16.55 

3 

27.71 

Woodland 

17.233 

12 

295.07 

Dixon 

17.233 

6 

207.17 

Totals  and  avgs 

.  19.76 

54 

1159.09 

1  Biggs  record. 

2  Red  Bluff  record. 

3  Davis  record. 

Years 
1913 

1913-14 

1913-14 

1914 

1913-14 

1913 


Average 

total 

depths  of 

water 

applied, 

ft. 

3.31 

5.15 

4.66 

1.83 

2.33 

2.94 

3.37 


Average 

total 

yields, 

tons  per 
acre 
6.19 
6.01 
6.26 
4.82 
6.45 
6.76 
6.08 


If  the  amount  of  water  used  on  Sacramento  Valley  farms,  as  indi- 
cated by  the  above  table,  were  to  be  taken  as  the  amount  necessary  to 
get  maximum  economic  yield,  it  is  evident  that  the  results  at  Davis 
would  not  be  applicable  throughout  the  valley.  The  amounts  of  water 
applied,  however,  do  not  necessarily  indicate  the  amounts  needed.  In 
many  cases  much  more  water  was  applied  than  was  retained  by  the 
soil;  and  in  the  case  of  the  compact  soils  about  Willows  it  was  not 
possible  to  get  into  the  soil  sufficient  water  to  supply  the  needs  of  the 
crop.  That  the  results  at  Davis  are,  in  general,  applicable  throughout 
the  valley,  with  the  exception  of  the  results  on  the  highly  pervious 
gravelly  loams  at  Orland  and  the  impervious  Tehama  clays  and  clay 
loams  at  Willows,  was  made  plain  from  the  approximately  11,000  soil- 
moisture  determinations  made  on  the  Sacramento  Valley  alfalfa  farms 
under  observation  during  three  years  of  the  investigations. 

At  Davis  the  amounts  of  water  used  were  strictly  under  control, 
and,  with  the  exception  of  the  plat  receiving  a  depth  of  60  inches, 
single  irrigations  were,  as  a  rule,  not  greater  than  the  soil  would  retain, 
the  soil-moisture  determinations  before  and  after  irrigation  showing 
that  an  average  of  76.4  per  cent  of  the  water  applied  to  plats  which 
were  given  a  depth  of  6  inches  in  one  irrigation  was  retained  in  the 
upper  6  feet  of  the  soil,  and  that  the  plats  given  iy2,  9,  and  12  inches 
per  irrigation,  making  an  average  of  9%  inches  per  application, 
retained  an  average  of  60.6  per  cent  in  the  upper  6  feet  of  soil  and  97.7 
per  cent  in  the  upper  12  feet.  The  soil  of  the  experimental  irrigation 
tract  at  Davis  is  chiefly  a  fine  sandy  loam,  relatively  uniform,  with  no 


280  UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION 

impervious  stratum,  and  with  the  ground  water  level  below  the  normal 
feeding  zone  of  the  plant  roots.  The  upper  two  feet  are  very  uniform, 
but  the  third  to  eighth  feet  are  of  fine  sandy  loam,  pocketed  at  irregu- 
lar intervals  with  coarse  sand  or  clay  loam.  While  at  Gridley  the  sur- 
face soil  of  the  fields  under  observation  in  1913  does  not  vary  greatly 
from  the  soil  at  Davis,  most  of  it  is  underlaid  with  hardpan  at  depths 
of  from  four  to  six  feet,  and  all  of  it  contained  free  ground  water  at  six 
feet  or  less  from  the  surface.  At  Los  Molinos,  while  the  soil  of  some 
of  the  fields  is  comparable  with  that  at  Davis,  being  of  silty  or  sandy 
loam  and  of  relatively  uniform  depth  for  at  least  12  feet  from  the  sur- 
face, some  fields  have  more  clay  and  some  are  more  gravelly  than  those 
at  Davis.  The  normal  rainfall  at  Red  Bluff,  which  is  the  nearest  point 
of  observation  to  Los  Molinos,  is  approximately  nine  inches  greater 
than  at  Davis,  and  in  the  years  1913  and  1914  it  was  more  than  six 
inches  above  the  average  at  Davis  for  the  six  years  covered  by  the 
experiments  there.  An  entirely  different  type  of  soil  is  found  at 
Orland,  all  but  one  of  the  fields  investigated  having  been  made  up 
largely  of  gravel.  Here,  also,  water  conditions  differ  considerably 
from  those  at  Davis,  a  shortage  of  water  in  the  late  season  in  1913 
having  made  it  necessary  to  eliminate  one  irrigation. 

A  very  wide  departure  in  soil  type  is  encountered  at  Willows,  and, 
as  indicated  by  the  summaries  of  use  on  fields  under  investigation 
there,  it  was  impossible  to  get  enough  water  into  the  soil  to  satisfy  the 
needs  of  the  crop.  While  the  soils  at  Woodland  are  generally  com- 
parable with  those  at  Davis,  paying  for  irrigation  water  on  a  quantity 
basis  rather  than  on  an  acreage  basis,  as  at  Gridley,  Los  Molinos,  Or- 
land, and  Willows,  altered  the  Woodland  practice  materially.  During 
the  season  of  1913  at  Woodland,  following  a  winter  of  low  rainfall, 
the  usual  practice  was  to  give  at  least  three  irrigations,  and  some  farms 
received  water  six  times,  alfalfa  bringing  good  prices  that  year,  and 
water  therefore  being  applied  plentifully.  In  1914,  however,  follow- 
ing a  winter  of  more  than  normal  rainfall,  and  when  the  price  of 
alfalfa  had  dropped  to  nearly  one-third  the  figure  obtainable  in  1913, 
no  irrigators  watered  more  than  three  times,  and  as  a  rule  only  two, 
with  many  not  watering  at  all.  Observations  were  made  at  Dixon 
during  1913  only.  Water  used  there  is  obtained  from  pumping  plants 
and  use  generally  represents  what  the  various  irrigators  consider  to 
be  necessary.  While  in  this  regard  conditions  at  Dixon  are  similar  to 
those  which  governed  the  experiments  at  Davis,  the  soil  is  considerably 
heavier  than  at  Davis,  and  takes  water  much  less  freely. 

Gridley. — Analyzing  the  results  obtained  at  Gridley,  it  was  found 
that  a  maximum  yield  of  9.38  tons  was  obtained  from  a  field  which 


IRRIGATION    OF    ALFALFA    IN    SACRAMENTO    VALLEY  281 

received  a  total  annual  depth  of  irrigation  water  of  31.6  inches,  but 
that  the  next  nearest  yield  was  only  7.28  tons  per  acre,  obtained  on  a 
field  which  received  34  inches  of  water  for  the  season.  Eight  out  of 
the  fourteen  fields  studied  at  Gridley  received  greater  annual  depths 
of  irrigation  water  than  34  inches,  but  on  three  of  these  the  yield  fell 
below  five  tons,  on  four  below  six  tons  per  acre,  and  on  seven  below 
seven  tons.  In  other  words,  after  eliminating  the  single  field  that 
had  the  excessive  yield  of  9.38  tons  per  acre,  it  was  found  that  the 
point  beyond  which  it  did  not  pay  to  add  to  the  depths  applied  cor- 
responds substantially  with  the  points  established  in  the  Davis  experi- 
ments, namely,  between  30  and  36  inches.  The  seasonal  rainfall  at 
Gridley  preceding  the  heaviest  of  these  yields  was  13.9  inches. 

Los  Molinos. — Analyzing  the  results  obtained  at  Los  Molinos  for 
the  seasons  1913  and  1914,  it  is  found  that  a  maximum  yield  of  8.31 
tons  per  acre  was  obtained  with  a  total  annual  application  of  47.4 
inches,  following  an  average  rainfall  for  the  two  seasons  of  approxi- 
mately 24.4  inches.  To  what  extent,  if  at  all,  excessive  use  here  re- 
duced yields  by  soil  leaching  can  only  be  conjectured.  Seven  of  the 
11  fields  under  observation  received  more  irrigation  water  than  the 
field  of  maximum  yield,  the  maximum  application  being  84  acre-inches 
per  acre.  Of  these  seven  fields,  however,  one  yielded  less  than  four 
and  one-half  tons  per  acre,  four  below  six  tons  per  acre,  and  six  below 
seven  tons  per  acre.  At  Los  Molinos  it  is  to  be  noted  that  both  the 
maximum  and  the  majority  of  applications  were  considerably  in  excess 
of  the  applications  at  Davis,  but,  as  pointed  out  in  the  discussion  of 
soil-moisture  determinations  in  this  area,  the  soils  of  the  Los  Molinos 
fields  are  highly  permeable  and  the  use  of  water  was  wasteful.  Studies 
of  the  underground  distribution  of  the  irrigation  water  applied  showed 
that  beyond  a  doubt  large  quantities  passed  below  a  depth  of  six  feet, 
single  applications  amounting,  in  numerous  cases,  to  between  20  and 
30  inches. 

Orland. — Averages  for  eight  fields  at  Orland,  where  the  soil  is 
prevailingly  gravelly,  gave  a  maximum  of  6.77  tons  per  acre,  with  a 
total  annual  application  of  24.6  inches  after  an  average  seasonal  rain- 
fall of  19.2  inches.  The  maximum  yield  at  Orland  was  obtained  on 
the  field  that  received  the  least  water,  the  yield  from  two  of  the  seven 
remaining  fields  falling  below  five  tons,  and  that  from  five  falling 
below  six  tons.  Of  the  whole  eight  fields  water  was  applied  in  excess 
of  80  inches  on  two  fields,  in  excess  of  55  inches  on  three  fields,  and  in 
excess  of  45  inches  on  five  fields. 

Willows. — With  complete  results  available  for  only  one  year  and 
from  only  three  fields  at  Willows,  but  with  these  results  verified  by 


282  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

special  studies  in  1915,  it  is  evident  that  the  results  are  in  no  way 
comparable  with  the  results  at  Davis,  this  being  due  to  the  ' '  tightness ' ' 
of  the  soil  of  the  Willows  fields  and  the  impossibility  of  getting  irri- 
gation water  into  it  in  amounts  sufficient  to  satisfy  the  plants.  A 
maximum  yield  of  only  5.39  tons  was  obtained  at  Willows  with  an 
application  of  23.6  inches  in  addition  to  the  seasonal  rainfall  of  ap- 
proximately 28.7  inches  for  the  preceding  winter.  Results  at  Willows 
indicate  plainly  that  the  soil-moisture  needs  of  alfalfa,  on  the  soils 
that  hold  moisture  so  tenaciously  as  do  those  at  Willows,  are  in  excess 
of  the  maximum  applications  found  in  1914.  Further,  it  is  plain  from 
the  special  studies  in  1915  that  to  irrigate  adequately  the  silty  clay 
loams  and  the  clay  adobes  of  the  Willows  area  water  must  be  applied 
frequently  and  in  small  quantities,  and  at  no  time  following  the  winter 
rainfall  must  the  soil  be  allowed  to  dry  out.  The  amount  of  water 
used  on  these  Tehama  clay  soils  is  sure  to  increase  as  improvement  in 
their  physical  condition,  due  to  cropping  and  cultivation,  makes  them 
more  pervious  to  water. 

Woodland. — Averages  for  the  12  fields  at  Woodland,  for  which 
full  records  are  available,  show  a  maximum  yield  of  8.81  tons  per  acre 
with  a  use  of  water  of  29.7  inches  in  addition  to  an  average  seasonal 
rainfall  of  18.3  inches.  Three  fields,  which  received  depths  of  23.5, 
33.1,  and  43.7  inches,  gave  respective  yields  of  7.60,  7.87,  and  8.04  tons 
per  acre.  Taking  seven  fields  for  which  the  yields  were  most  nearly 
equal,  the  range  of  variation  being  slightly  over  two  tons  and  the 
average  yield  being  6.93  tons  per  acre,  the  average  use  was  found  to 
be  a  depth  of  30.7  inches.  Thus  at  Woodland  it  is  found  also  that 
the  usual  maximum  use,  taking  an  average  of  one  wet  and  one  drv 
season,  does  not  depart  widely  from  that  found  most  satisfactory  at 
Davis ;  also  that  the  maximum  average  yield  for  one  field  during  the 
two  years  of  record  was  obtained  with  slightly  less  than  30  inches. 

Dixon. — Here  the  largest  yield  in  the  single  year  of  observation 
was  9.97  tons  per  acre  with  a  total  depth  of  irrigation  of  37.7  inches, 
in  addition  to  a  seasonal  rainfall  of  7.31  inches.  The  average  use  for 
six  fields,  from  which  complete  records  are  available,  was  35.3  inches, 
or  again  in  close  agreement  with  the  Davis  experiments. 

The.  allowance  necessary  to  be  made  for  difference  in  local  soil 
conditions  and  irrigation  practice  is,  it  is  believed,  fully  established 
by  the  comparisons  made  above.  In  general,  as  already  indicated,  the 
statement  is  justified  that  the  six-year  record  for  Davis  is  applicable 
throughout  the  valley  except  to  the  very  open  soils  such  as  those 
around  Orland,  and  the  silty  clays  and  clay  adobes  found  in  these 
investigations  in  the  neighborhood  of  Willows,  but  also  existing  else- 


IRRIGATION    OF    ALFALFA    IN    SACRAMENTO    VALLEY  283 

where  in  considerable  areas.  The  average  for  Willows  indicates,  as 
already  pointed  out,  that  total  irrigations  of  less  than  24  inches  per 
season  are  insufficient  for  satisfactory  yields,  while  the  results  at 
Orland  indicate  that  applications  averaging  in  excess  of  48  inches  per 
year,  while  sometimes  difficult  to  overcome  on  the  very  gravelly  soils, 
do  not  give  corresponding  increases  in  tonnage.  The  average  use  at 
Woodland,  which  was  below  that  at  either  Dixon  or  Gridley,  was 
plainly  a  result  of  paying  for  irrigation  water  on  a  quantity  rather 
than  on  a  flat  acreage  basis.  Finally,  the  average  at  Gridley  illus- 
trates what  may  be  expected  on  the  open  loam  soils  underlaid  with 
hardpan  or  ground  water. 

INVESTIGATIONS  ON  EXPEEIMENTAL  TRACT  AT  WILLOWS 

Investigations  on  alfalfa  farms  near  Willows  in  1913  and  1914 
disclosed  a  relatively  small  use .  of  irrigation  water  and  correspond- 
ingly low  yields  of  hay.  Soil  borings  soon  made  it  evident  that  irri- 
gation water  was  not  penetrating  sufficiently  deeply  into  the  soil  to 
meet  the  needs  of  the  alfalfa  plants.  In  some  cases  irrigators  who 
considered  that  they  were  applying  an  ample  quantity  of  water  were 
in  fact  wetting  only  the  upper  ten  or  twelve  inches  of  soil,  whereas 
normally  at  least  the  upper  four  to  six  feet  should  have  had  water. 

The  heavy  soils  encountered  in  the  investigations  around  Willows 
are  classified  in  the  soil  survey  as  Tehama  clay  and  clay  loam.3  These 
soils  are  all  of  compact  structure  and  inclined  to  be  refractory,  very 
sticky  when  wet,  and  subject  to  hard  baking  when  drying. 

As  indicated  in  table  No.  4  above,  the  average  use  of  water  on  three 
farms  at  Willows  in  1914  was  1.83  acre-feet  per  acre,  and  the  average 
yield  on  six  farms  there  in  1914  was  only  4.82  tons  per  acre.  In  no 
single  case  was  more  than  1.97  acre-feet  of  water  per  acre  applied  per 
season,  and  none  of  the  measured  yields  of  alfalfa  exceeded  5.39  tons 
per  acre. 

For  the  purpose  of  ascertaining  if  more  frequent  irrigations  would 
improve  conditions  on  these  heavy  soils,  a  field  of  8.75  acres  about 
five  miles  northeast  of  Willows  was  utilized  for  experimental  purposes 
during  the  season  of  1915.  This  field  was  already  in  alfalfa  and 
carried  one  of  the  best  stands  to  be  found  in  the  immediate  neighbor- 
hood. The  field  was  divided  into  twenty-one  border  checks,  60  feet 
wide  by  300  feet  long,  having  an  average  grade  of  four  inches  per  one 
hundred  feet  and  an  average  area  per  check  of  0.42  acre. 

3  U.  S.  Dept.  Agr.,  Bureau  of  Soils,  Reconnoissance  Soil  Survey  of  Sacramento 
Valley,  California. 


284  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

The  soil  in  this  field,  which  is  classed  as  a  Tehama  clay  loam,  is 
grayish  in  color  and  of  compact  structure  and  refractory  nature. 
When  wet  it  is  sticky,  and  upon  drying  becomes  very  hard,  but  does 
not  check  or  crack.  It  is  free  from  both  hardpan  and  gravel  and 
little  difference  is  noticeable  between  the  soil  and  subsoil.  This  type 
of  soil  was  selected  because  the  soil  survey  maps  indicate  the  presence 
of  about  45,000  acres  of  it  in  the  Sacramento  Valley,  very  largely  east 
of  Willows  in  the  area  surrounding  this  field. 

The  amount  of  water  used  on  each  of  the  plats  during  the  season 
was  two  acre-feet  per  acre,  an  average  irrigation  head  of  2.82  cubic 
feet  per  second  being  generally  divided  between  two  checks,  although 
various  other  sizes  of  heads  were  tried.  One-third  of  the  twelve 
checks  under  observation  were  irrigated  with  a  depth  of  six  inches, 
once  for  each  cutting  except  the  last,  one-third  received  two  three- 
inch  irrigations  between  cuttings  applied  just  before  and  just  after 
the  crop  was  removed,  and  one-third  received  three  two-inch  irriga- 
tions, at  intervals  of  about  12  days.  All  of  the  water  entering  the 
field  was  measured  by  a  21/^-foot  rectangular  weir  and  automatic 
register. 

For  the  purpose  of  increasing,  if  possible,  the  perviousness  of  the 
soil  to  water,  two  checks  were  treated  with  ground  limestone  at  the 
beginning  of  the  season  at  the  rate  of  four  tons  per  acre.  It  was 
not  expected  that  these  checks  would  show  much  change  the  first  year, 
and  they  did  not.  The  largest  annual  yield  of  alfalfa,  5.07  tons  per 
acre,  was  obtained  from  the  checks  receiving  three  two-inch  irrigations 
per  cutting,  an  increase  of  18  per  cent  over  the  lowest  yields,  4.42  tons 
per  acre,  being  secured  from  the  checks  that  received  two  three-inch 
irrigations  per  cutting,  and  lowest  yield,  4.29  tons  per  acre,  coming 
from  the  checks  irrigated  with  one  six-inch  irrigation  per  cutting. 

While  the  above  increases  of  yield  indicate  the  desirability  of  more 
than  one  irrigation  per  cutting,  the  differences  in  the  one  season  of 
investigations  were  not  great.  It  was  evident  to  those  in  the  field, 
however,  that  the  more  frequent  the  application  of  water  the  better 
the  moisture  condition  of  the  soil.  Borings  for  soil-moisture  determi- 
nations were  difficult,  except  immediately  after  irrigations,  and  even 
then  difficulty  was  encountered  below  the  first  foot  of  soil.  Including 
the  12  plats,  a  total  of  3408  moisture  determinations  were  made  before 
and  after  irrigations,  and  while  the  chief  value  of  these  is  in  the 
larger  understanding  they  give  of  the  character  of  these  compact  soils, 
especially  with  reference  to  the  permeability  to  irrigation  water  they 
substantiate,  to  the  extent  reasonably  to  be  expected,  the  better  results 
due  from  the  more  frequent  applications  of  irrigation  water. 


IRRIGATION    OF    ALFALFA    IN    SACRAMENTO   VALLEY  285 

In  order  to  gain  an  idea  of  the  root  development  of  the  alfalfa  in 
this  field,  a  hole  about  six  feet  square  and  three  feet  deep  was  ex- 
cavated. This  also  afforded  a  good  view  of  the  cross-section  of  the  soil 
formation.  The  roots  of  the  plants  were  carefully  removed.  It  was 
found  that  the  taproots  of  the  alfalfa  were  not  over  one-half  inch  in 
diameter  and  did  not  extend  below  a  depth  of  three  feet.  The  main 
mass  of  the  roots  was  concentrated  in  the  upper  two  feet  of  soil.  The 
fact  that  the  greater  part  of  the  alfalfa  plants  in  this  particular  field 
are  shallow-rooted  is  attributed  largely  to  the  compact  structure  of  the 
soil,  making  moisture  penetration  difficult. 

After  removing  the  soil  for  root  examination  some  rather  sur- 
prising results  were  found  in  tests  made  by  filling  the  hole  from  which 
they  came  with  water  and  noting  the  time  required  for  downward  and 
lateral  percolation.  Twenty-four  hours  after  the  hole  had  been  filled 
to  a  depth  of  three  feet  there  remained  in  the  hole  two  feet  of  water. 
Two  weeks  later  there  still  remained  one  foot.  Holes  two  inches  in 
diameter  and  four  feet  deep  bored  12  inches  away  from  the  large  test 
hole  showed  no  lateral  percolation.  In  holes  bored  six  inches  from 
the  test  hole  a  slight  amount  of  water  had  seeped  through  after  12 
hours.  Later  another  hole  was  excavated  in  a  different  part  of  the 
field  and  similar  trials  made,  practically  the  same  results  being  secured 
as  in  the  first  test.  These  tests  serve  to  show  the  impermeability  and 
peculiar  physical  conditions  of  the  soil  represented  in  this  field. 

QUANTITIES     OF     WATER     TO     APPLY     TO     SACRAMENTO     VALLEY 

ALFALFA  FIELDS  AT  SINGLE  IRRIGATIONS  AS  DETERMINED 

BY  THE  CAPACITY  OF  THE  DIFFERENT  SOILS 

TO  RETAIN  WATER 

At  the  outset  of  the  investigations,  one  of  the  important  practical 
questions  presented  was,  How  much  irrigation  water  applied  at  one 
time,  and  added  to  that  already  present  in  the  soil  at  the  time  of 
irrigation,  would  the  various  soils  of  Sacramento  Valley  retain  ?  While 
no  particular  effort  was  made  in  the  investigations  to  ascertain  how 
much  irrigation  water  the  various  soils  encountered  would  hold  during 
the  actual  process  of  irrigation,4  it  was  desired  to  ascertain  how  much 
would  be  retained  after  any  surplus  should  pass  through  the  soil; 
or,  in  other  words,  how  much  of  the  water  applied  would  be  retained 
against  gravity.  As  the  amount  retained  would  depend  largely  upon 
the  size  of  the  soil  particles,  it  was  deemed  best  to  have  mechanical 
analyses  made  of  the  soil  from  a  number  of  the  fields  under  obser- 
vation.    This  was  done  by  the  Division  of  Soil  Technology  of  the 

4  This  was  however,  indirectly  ascertained  through  ' '  pore  space ' '  determinations. 


286  UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION 

College  of  Agriculture  of  the  University  of  California.  Further,  as 
the  quantity  of  water  soils  will  absorb  and  the  rapidity  with  which  it 
is  absorbed  depend  to  a  considerable  degree  on  the  compactness  of  the 
soil,  and,  in  order  to  determine  what  portion  of  the  water  applied  in 
irrigation  was  retained  by  the  soil,  it  was  necessary  to  ascertain  the 
volume  weight  of  the  soils  "in  place."  This  was  done  partly  by 
standard  laboratory  methods,  but  chiefly  by  a  special  field  method 
devised  in  the  course  of  the  investigations,  and  found  to  conform 
within  satisfactory  limits  to  other  methods  commonly  used  by  investi- 
gators in  more  precise  experiments.5 

The  principal  work  in  tracing  the  underground  distribution  of  the 
irrigation  water  was  done  on  fifteen  fields — two  at  Gridley,  four  at 
Los  Molinos,  one  at  Orland,  two  at  Willows,  five  at  Woodland,  and 
one  at  Dixon.  With  the  possible  exception  of  one  of  the  fields  at 
Woodland  and  the  two  fields  at  Willows,  the  soil  sampling  indicated 
that  the  capacity  of  the  soil  to  retain  water,  assuming  sufficient  under- 
drainage  to  carry  off  the  free  water  in  the  soil,  was  satisfied.  A 
careful  analysis  of  the  results  of  the  soil  sampling  and  moisture  de- 
terminations brings  out  the  following  facts  that  should  be  of  practical 
interest  to  irrigators. 

1.  Pour  times  as  much  water  was  applied,  on  the  average,  to  the 
silt  loam  soils  with  fine  sandy  loam  subsoils  as  it  was  possible  to  apply, 
on  the  average,  to  the  compact  clay  soils  of  the  experimental  tract  at 
Willows,  and  more  than  three  times  as  much  as  was  applied  to  the 
clay  soils  of  two  of  the  fields  at  Willows. 

2.  Only  about  one-third  of  the  water  applied  to  the  silt  loam  soils, 
as  represented  by  five  fields,  was  retained  for  the  use  of  the  alfalfa 
plants  in  the  upper  six  feet  of  the  soil,  where  the  principal  root 
development  is  located. 

3.  In  the  case  of  none  of  the  15  fields  under  observation  did  the 
amount  of  water  retained  per  irrigation  in  the  upper  six  feet  of  soil 
exceed  8.20  acre-inches  per  acre,6  and  in  only  two  cases  of  the  15  did 
it  exceed  six  acre-inches. 


s  The  method  followed  consisted  in  weighing  all  of  the  soil  taken  from  holes 
carefully  bored  with  a  two-inch  posthole  type  soil  auger  and  then  ascertaining 
the  volume  of  this  soil  as  it  was  "in  place"  by  the  use  of  a  thin  rubber  tube 
inserted  in  the  hole  and  filled  with  a  known  quantity  of  water.  This  method 
was  ' '  checked ' '  against  the  laboratory  method  by  use  of  the  Bowman  soil 
compactor,  the  iron  cylinder,  and  the  paraffin  methods  as  applied  to  soils  in 
place  in  a  series  of  experiments  conducted  by  Mr.  O.  W.  Israelsen  of  this  investi- 
gation and  Professor  Charles  F.  Shaw  of  the  Division  of  Soil  Technology  of  the 
College  of  Agriculture  of  the  University  of  California. 

6  Clay  loam  strata  at  depths  varying  from  eight  to  ten  feet  caused  partial 
waterlogging  in  overlying  soil,  hence  the  figure  8.20  is  unusually  high.  All  of 
the  water  in  this  soil  was  not  retained  against  gravity. 


IRRIGATION   OF    ALFALFA    IN    SACRAMENTO    VALLEY  287 

4.  In  only  two  cases  out  of  ten  in  connection  with  the  clay  soils 
did  the  water  that  was  absorbed  by  the  upper  six  feet  of  soil  reach  four 
acre-inches  per  acre,  in  only  three  cases  did  it  exceed  three  acre-inches 
per  acre,  and  in  four  cases  it  was  less  than  two  acre-inches  per  acre. 

5.  The  average  quantities  of  water  retained  per  acre-foot  of  soil  per 
irrigation  were  0.92  acre-inch  for  the  silt  loams  with  fine  sandy  loam 
subsoils,  0.71  acre-inch  for  the  silt  loams  without  fine  sandy  loam  sub- 
soils, 0.58  acre-inch  for  the  clay  loams,  and  0.37  acre-inch  for  the  clays, 
not  including  the  experimental  tract  at  Willows,  in  every  case  less  than 
one  acre-inch  per  acre-foot  of  soil. 

6.  The  maximum  average  quantities  of  water  retained  by  the  upper 
six  feet  of  soil  per  acre-foot  per  irrigation  were  1.02  acre-inches  for 
the  silt  loams  with  fine  sandy  loam  subsoils,  0.75  acre-inch7  for  the  silt 
loams  without  fine  sandy  loam  subsoils,  0.78  acre-inch  for  the  clay 
loams,  and  0.49  acre-inch  for  the  clays. 

7.  Counting  only  the  fields  in  which  the  full  capacity  of  the  soils 
to  retain  water  against  gravity  was  satisfied,  i.e.,  all  of  the  fields  having 
loam  soils  except  one  field  at  "Woodland,  the  average  water  retained 
per  irrigation  in  the  upper  six  feet  of  soil  was  4.31  acre-inches  per 
acre,  or  only  32.6  per  cent  of  the  average  individual  applications,  and 
only  0.72  acre-inch  per  acre-foot  of  soil. 

8.  Assuming  that  in  every  case  the  surface  foot  of  soil  received  at 
each  irrigation  sufficient  water  to  satisfy  its  full  capacity  to  retain  water 
against  gravity,  it  is  found  from  the  detailed  data  at  hand  that  the 
average  for  the  18  fields,  including  the  experimental  tract  at  Willows, 
was  1.23  acre-inches  per  acre,  and  that  the  averages  for  the  different 
soil  types  were  1.08  acre-inches  per  acre  for  the  silt  loams,  1.35  acre- 
inches  per  acre  for  the  clay  loams,  and  1.35  acre-inches  per  acre  for 
the  clays.  Therefore,  in  the  case  of  the  typical  silt  loam  soils  of  the 
Sacramento  Valley,  assuming  one  irrigation  per  cutting,  single  appli- 
cations of  irrigation  water  exceeding  a  depth  of  one  to  one  and  one- 
half  inches  per  foot  in  depth  of  the  soil  it  is  necessary  to  moisten, 
accomplish  no  useful  purpose.  The  typical  clay  loams  and  clays  of 
Sacramento  Valley,  in  their  normal  condition  of  moisture,  will  absorb 
and  hold  against  gravity  as  much  as  one  and  one-fourth  to  one  and 
three-fourths  inches  in  depth  of  irrigation  water  per  foot  of  soil  it  is 
necessary  to  moisten;  however,  that  amount  of  water  will  not  be 
absorbed  by  these  soils  unless  it  is  applied  very  slowly.8 

7  Not  counting  the  field  on  which  8.20  acre-inches  per  acre  were  retained 
because  of  abnormal  conditions  previously  referred  to. 

8  It  is  of  interest  here  to  note  that  with  the  surface  foot  of  soil  filled  to  its 
capacity  to  retain  water  against  gravity  the  percentages  of  the  pore  space  of 
the  soil  filled  were  as  follows:  for  the  silty  loam  soils,  from  37  to  55  and  averaging 


288  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

It  seems  evident  from  the  figures  given  above  that  there  is  much 
ground  for  improvement  in  the  matter  of  the  quantity  of  water  to 
apply  to  the  alfalfa  fields  of  Sacramento  Valley  at  single  irrigations. 
Had  it  been  feasible  to  carry  the  soil-moisture  determinations  to  a 
greater  depth  than  six  feet,  the  extent  of  the  waste  resulting  from  the 
large  single  applications  would  be  still  clearer.  The  data  obtained 
are,  however,  sufficient  to  show  clearly  that  the  prevailing  practice 
on  Sacramento  Valley  alfalfa  fields  is  to  apply  far  more  water  at  single 
irrigations  than  the  more  open  soils  have  capacity  to  retain  and  than 
the  more  compact  clay  soils  absorb  under  methods  of  application 
followed. 

A  significant  comparison  can  be  made  between  the  amounts  of 
water  retained  by  the  soil  in  the  case  of  the  15  typical  Sacramento 
Valley  alfalfa  farms  and  the  amounts  retained  in  the  case  of  six  of 
the  plats  on  the  experimental  tract  at  Davis,  where  the  applications 
of  water  were  under  definite  control.  The  average  depth  of  water 
applied  per  irrigation  to  these  six  plats  was  7.75  inches  and  the  average 
quantity  retained  in  the  upper  six  feet  of  soil  in  the  years  1913,  1914, 
and  1915  was  4.59  acre-inches  per  acre,  or  66.8  per  cent  of  the  amount 
applied.  On  some  of  these  plats,  however,  the  borings  for  soil-moisture 
determinations  were  made  to  a  depth  of  12  feet,  and  it  was  found 
that  within  this  depth  practically  all  of  the  water  applied  was  retained 
for  the  benefit  of  the  plants.  The  average  amount  of  water  added 
by  irrigation  to  the  surface  foot  of  soil  in  the  Davis  experiments  was 
1.45  acre-inches  per  acre.  In  other  words,  from  the  standpoint  merely 
of  the  capacity  of  such  deep  loam  soil  as  that  at  Davis  to  retain  irri- 
gation water  against  gravity,  and  assuming  that  the  lower  depths  will 
' '  take  up  "  as  much  water  as  the  surface  foot,  the  application  once  per 
cutting  of  one  and  one-half  acre-inches  of  water  per  acre-foot,  of  soil 
it  is  desired  to  moisten,  is  not  excessive. 


DESIRABLE  IRRIGATION  "HEADS"  FOR  SACRAMENTO  VALLEY 
ALFALFA  FIELDS 

In  any  investigation  of  the  proper  duty  of  water  the  size  of  the 
irrigation  heads  used  and  its  relation  to  the  type  of  soil  irrigated,  the 
method  of  irrigation  followed,  and  the  size  and  slope  of  the  individual 
areas  watered  with  a  single  head  are  always  important.  Fields  may  be 
evenly  surfaced  and  levees  perfectly  made  and  proportioned,  and  yet 
the   result  will   be   excessive   waste  or  inadequate  absorption  if  the 


45.5;  for  tlie  clay  loam  soils,  from  51  to  71  and  averaging  62.2;  for  the  clay  soils, 
from  57  to  74  and  averaging  65.5;  and  for  all  of  the  fields  combined,  54.5. 


IRRIGATION    OF    ALFALFA    IN    SACRAMENTO    VALLEY  289 

stream  of  water  turned  into  each  check  is  either  too  large  or  too  small. 
The  discussion  as  to  what  became  of  the  water  applied  on  a  number 
of  Sacramento  Valley  alfalfa  fields,  already  presented,  showed  that 
where  large  quantities  were  applied  to  the  open  loam  soils  at  single 
irrigations  much  of  the  water  passed  below  the  principal  rooting  zones 
of  the  alfalfa  plants,  and  that  the  usual  practice  followed  in  irrigating 
the  clay  soils  failed  to  accomplish  sufficient  penetration  by  the  water. 
The  stabilizing  of  the  irrigation  heads  used  in  Sacramento  Valley, 
with  direct  reference  to  the  size  of  checks  and  the  character  of  the  soil, 


Fig.  2. — A  thoroughly  prepared  alfalfa  field  ready  for  final  harrowing  and  seed- 
ing.    These  checks  do  not  exceed  500  feet  in  length  or  40  feet  in  width. 

is  obviously  one  of  the  very  important  irrigation  problems  of  the  valley. 
Quite  extensive  experiments  and  observations  will  be  necessary  for 
furnishing  a  satisfactory  basis  for  fully  understanding  this  problem, 
but  the  collection  of  some  information  bearing  on  the  question  was 
accomplished  during  the  investigations  in  1913  and  1914.  This  infor- 
mation was  obtained  from  twenty -five  fields — three  at  Gridley,  two  at 
Los  Molinos,  five  at  Orland,  two  at  Willows,  nine  at  Woodland,  three 
at  Davis,  and  one  at  Dixon.  Five  classes  of  soil  were  covered — gravelly 
loams,  three  fields ;  sandy  loams,  four  fields ;  silt  loams,  nine  fields ; 
clay  loams,  six  fields ;  and  clays,  ^.\e  fields.  Observations  of  the  under- 
ground distribution  of  the  water  applied  were  made  in  connection  with 
ten  of  the  fields. 


290  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

From  an  investigation  of  the  data  gathered  in  these  investigations, 
it  is  evident  that  the  most  desirable  head  of  water  to  use  on  any  given 
soil  can  not  be  adequately  determined  by  comparing  use  on  different 
fields.  The  present  general  practice  in  Sacramento  Valley,  expressed 
in  cubic  feet  per  second  per  acre,  is,  however,  satisfactorily  indicated 
from  the  average  figures  obtained,  namely,  23  for  gravelly  loams, 
10.9  for  sandy  loams,  8.8  for  silt  loams,  7.3  for  clay  loams,  and  3.2  for 
clays.  The  difficulty  of  irrigating  porous  soils  with  small  heads  and 
of  irrigating  clay  soils  with  large  heads  is  well  recognized  among 
irrigators,  even  if  the  most  satisfactory  relationships  have  not  been 
worked  out  in  detail. 

While  a  comparison  of  the  rates  of  application  on  the  different 
fields  as  given  above  fails  to  disclose  the  best  size  of  head  to  use,  a 
comparison  of  the  relation  between  irrigation  heads  and  depths  of 
application  on  single  fields  makes  it  plain  that  in  many  cases  either 
the  head  should  be  increased  or,  even  better,  the  area  of  the  checks 
reduced. 

Summarizing  the  rates  and  depths  of  application  at  different  irri- 
gations of  five  individual  fields,  it  was  found,  with  minor  exceptions, 
that  in  each  instance,  where  the  soil  was  sandy  loam  or  silt  loam,  the 
depth  of  water  applied  increased  as  the  rate  of  application  decreased. 
In  one  case,  due  to  the  use  of  a  relatively  small  head,  a  depth  of 
3.03  feet  of  irrigation  water  was  used  before  the  surface  of  the  field 
was  flooded.  In  four  cases  more  than  2  feet  in  depth  was  applied  per 
irrigation,  and  in  fourteen  cases  out  of  twenty-seven  the  depth  of 
application  at  each  irrigation  exceeded  one  foot. 

In  order  to  carry  this  matter  further,  measurements  of  the  amount 
of  water  required  to  cover  a  one-acre  check,  having  a  slope  of  3% 
inches  per  one  hundred  feet,  when  applied  at  different  rates  were  made 
at  Davis.    The  data  obtained  were  as  follows : 


Rate  of 

application, 

cu.  ft.  per  sec. 

per  acre 

4.6 

Depth 

of  water 

required, 

ft. 

2.75 

10.1 

1.86 

13.5 

1.16 

15.3 

0.84 

17.8 

0.69 

Until  the  proper  relation  between  irrigating  heads  and  size  of 
checks  is  satisfactorily  worked  out  in  Sacramento  Valley  soil,  there 
is  sure  to  be,  there  as  well  as  elsewhere,  much  difference  of  opinion 
as  to  whether  small  checks  and  correspondingly  small  irrigation  heads 
or  large  checks  and  correspondingly  large  irrigation  heads  should 


IRRIGATION    OF    ALFALFA    IN    SACRAMENTO    VALLEY  291 

prevail  in  the  irrigation  of  alfalfa.  Those  who  favor  large  checks  and 
large  heads  base  their  preference  chiefly  on  the  greater  rapidity  with 
which  irrigation  can  be  accomplished  with  large  heads,  and  also  on 
the  assumed  lesser  cost  of  preparing  the  land  for  irrigation.  As  a 
rule,  where  large  heads  are  available  they  are  used,  and  in  some  cases, 
as  pointed  out  in  connection  with  the  heavy  soils,  especially  the  ' '  water- 
tight" soils  found  in  some  portions  of  the  Willows  area,  the  heads 
were  plainly  larger  than  they  should  be.  In  the  case  of  individual 
pumping  plants,  which  rarely  discharge  more  than  one  or  two  cubic 
feet  per  second,  checks  necessarily  are  small.  That  waste  of  land  goes 
with  the  large  field  ditches  necessary  in  carrying  large  heads,  and  also 
that  extravagant  notions  of  use,  and  a  greater  waste  when  breaks  occur 
with  large  heads,  are  sound  arguments  in  favor  of  small  heads,  can 
not  be  doubted.  Thoughtful  consideration  by  irrigators  and  intelli- 
gent advice  by  public  agencies  in  time  will  work  out  that  relationship 
which  best  will  serve  both  irrigators  and  the  public.  In  the  mean- 
time, it  is  very  clear  that  irrigators  should  bear  in  mind  the  fact  that 
the  irrigation  head  should  not  be  a  constant  quantity,  but  should  be 
varied,  where  practicable,  with  the  different  soils  found  on  nearly 
every  farm. 

Dimensions  and  grades  of  alfalfa  checks  vary  somewhat  in  the  six 
sections  of  Sacramento  Valley  studied.  Some  square  and  rectangular 
checks  are  used  in  each  section,  but  border  or  "strip"  checks  are  most 
common,  except  on  gravelly  soils  at  Orland,  where  the  most  satisfac- 
tory check  probably  is  one  about  100  feet  square,  containing  a  little 
under  one-fourth  acre,  and  with  each  check  having  direct  access  to  a 
field  lateral  to  do  away  with  carrying  water  to  one  check  over  another. 
The  border  checks  range  from  30  to  120  feet  in  width  and  from  60  to 
1750  feet  in  length,  the  most  usual  width  being  from  30  to  50  feet  and 
the  most  usual  length  from  400  to  700  feet.  The  grades  of  border 
checks  range  from  0.6  to  12  inches  per  100  feet  and  average  3.6  inches 
per  100  feet. 


DESIRABLE  MOISTURE  PERCENTAGES  FOR  ALFALFA  IN  SACRAMENTO 

VALLEY  SOILS  AND  THE  EFFECT  OF  VARIATION  IN  SOIL 

MOISTURE  ON  RATES  OF  ALFALFA  GROWTH 

In  interpreting  the  results  of  the  large  number  of  soil-moisture 
determinations  made  at  Davis  and  on  Sacramento  Valley  alfalfa  farms 
from  1913  to  1915,  account  has  been  taken  of  the  moisture  percentages 
found  as  related  to  the  percentages  at  which  the  plants  would  wilt,  and 


292  UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION 

also  of  the  effect  of  the  variation  in  those  percentages  on  the  growth 
of  the  alfalfa.  The  percentages  at  which  the  plants  wilt,  or  the 
■ '  wilting  coefficients, ' '  have  been  computed  on  the  basis  of  the  experi- 
ments of  Messrs.  Briggs  and  Shantz  of  the  Bureau  of  Plant  Industry 
of  the  United  States  Department  of  Agriculture.9  As  indicated  by 
these  experiments,  the  wilting  percentage  may  be  stated  to  be  the  point 
below  which  moisture  in  the  soil  ceases  to  be  available  to  the  plants, 
or,  at  least,  below  which  it  is  obtained  only  with  great  difficulty.  Due 
largely  to  the  difference  in  the  size  of  the  soil  particles,  plants  will 
wilt  in  clay  soils  when  there  is  still  an  amount  of  moisture  that  in 
sandy  soils  would  be  ample  for  all  plant  requirements. 

Determination  of  the  wilting  percentage  of  the  soil  was  made  for 
eight  of  the  experimental  plats  at  Davis,  six  of  the  experimental  plats 
at  Willows,  and  eleven  of  the  Sacramento  Valley  alfalfa  farms. 
Grouping  the  figures  obtained,  by  soils,  the  average  wilting  percent- 
ages found  were  as  follows :  silt  loams  with  fine  sandy  loam  subsoils, 
10.65 ;  other  silt  loams,  13.12 ;  clay  loams,  14.21 ;  clays,  13.06. 

In  other  words,  it  is  necessary  that  at  least  the  percentages  of 
moisture  indicated  shall  be  present  in  these  soils  at  all  times  in  the 
growing  season  if  the  plants  are  to  be  kept  from  wilting. 

It  must  be  noted,  however,  that  in  addition  to  these  percentages 
of  soil  moisture  that  are  necessary  to  prevent  wilting,  additional  quan- 
tities must  be  present  in  order  to  produce  satisfactory  growth.  Such 
additional  amounts  constitute  the  "available"  moisture  present  in 
the  soil. 

Obviously,  it  is  impossible  to  disregard  the  numerous  soil  and 
climatic  factors  other  than  soil  moisture  that  affect  the  yields  of 
alfalfa,  and  then  to  expect  the  yields  and  moisture  percentages  to  be 
consistent  throughout.  However,  by  grouping  the  yields  above  eight 
tons  per  acre,  from  six  tons  to  eight  tons  per  acre,  and  below  six  tons 
per  acre,  it  is  possible  to  approximate  the  best  or  "optimum"  per- 
centage of  available  moisture  over  and  above  the  amount  necessary  in 
each  soil  to  prevent  wilting. 

Assuming  the  yields  over  six  tons  per  acre  to  have  been  produced 
on  soil  having  at  least  as  much  as  the  ' '  optimum ' '  percentage  of  avail- 
able moisture,  the  data  indicate  that  the  "optimum"  for  Sacramento 


9  U.  S.  Dept.  Agr.,  Bureau  of  Plaut  Industry  Bulletin  230.  The  wilting  per- 
centages, or  "wilting  coefficients,"  for  the  Sacramento  Valley  soils  are  based 
on  the  ' '  moisture  equivalents ' '  of  those  soils,  as  determined  in  the  laboratory 
of  the  Division  of  Soil  Technology  of  the  College  of  Agriculture  of  the  University 
of  California  in  the  course  of  these  investigations.  It  might  be  noted  here  that 
the  moisture  equivalents  are  the  percentages  of  moisture  retained  in  the  soil 
after  the  soil  has  been  subjected  to  a  centrifugal  force  equal  to  1000  times  the 
force  of  gravity. 


IRRIGATION    OF    ALFALFA    IN    SACRAMENTO    VALLEY  293 

Valley  conditions  ranges  between  about  3  per  cent  and  about  7  per  cent 
and  averages  about  5  per  cent  above  the  wilting  percentage. 

For  one  of  the  fields  at  Los  Molinos  and  one  of  the  plats  at  Davis, 
on  both  of  -which  an  excess  of  irrigation  water  was  applied,  the  average 
available  percentage  was  8.91,  or  well  above  the  "optimum".  On  the 
other  hand,  the  average  percentage  of  available  moisture  on  six  ex- 
perimental plats  at  Willows,  four  plats  at  Davis,  one  field  at  Woodland, 
and  one  field  at  Willows,  for  which  either  the  application  or  the  ab- 
sorption of  irrigation  water  was  plainly  deficient,  was  only  1.02,  or 
well  below  the  "optimum". 

The  percentages  of  moisture  that  must  be  present  in  the  various 
Sacramento  Valley  soils  dealt  with  in  order  to  prevent  wilting  are 
believed  to  be  of  value  because  they  indicate  to  Sacramento  Valley 
irrigators  not  only  the  difference  between  the  clay  or  "heavy"  soils 
and  the  loams  and  sandy  soils  as  regards  the  amount  of  soil  moisture 
needed  to  prevent  wilting,  but  -also  that  for  all  of  the  soils  the  wilting 
percentage  is  higher  than  farmers  usually  suppose. 

If  one  could  assume  an  absolutely  dry  soil  it  might  be  convenient 
for  irrigators-  to  know  that,  as  disclosed  in  the  investigations,  the 
amount  of  water  necessary  to  supply  the  wilting  percentage  is  ap- 
proximately the  equivalent  of  about  one  and  two-thirds  inches  of 
rainfall  per  foot  of  depth  of  soil  in  which  the  crop  is  growing,  in  the 
case  of  the  silt  loams  with  fine  sandy  loam  subsoils,  of  about  two  inches 
in  the  case  of  the  other  silt  loams,  of  about  two  and  one-fourth  inches 
in  the  case  of  the  clay  loams,  and  of  two  and  three-fourths  inches  or 
more  in  the  case  of  clays  such  as  those  found  at  Willows.10 

In  other  words,  with  an  absolutely  dry  silt  loam  soil  eight  feet  deep 
the  first  16  inches  of  irrigation  water  would  no  more  than  supply  the 
amount  of  moisture  necessary  to  keep  deep-rooting  plants  from  wilt- 
ing; or,  expressed  still  differently,  with  such  a  soil  wholly  devoid  of 
moisture,  the  equivalent  of  a  rainfall  of  two  inches  for  each  one  foot 
depth  of  soil  the  crop  utilizes  would  need  to  be  supplied  before  the 
roots  of  the  crop  could  begin  to  utilize  the  moisture. 

Fortunately  an  absolutely  dry  soil  is  rarely  found  in  the  Sacra- 
mento Valle}^,  even  at  the  end  of  the  summer  season,  and  except  in 
very  dry  years  the  soils  of  the  valley  are  not  likely  to  begin  the  spring 
growing-season  with  less  soil  moisture  than  the  wilting  percentage. 

10  The  soil-moisture  studies  in  connection  with  the  clay  soils  at  Willows  dis- 
closed lower  wilting  percentages  and  lower  capacities  to  absorb  irrigation  water 
than  were  to  have  been  expected.  It  is  not  intended  to  discuss  this  technical 
phase  of  the  subject  in  the  present  report,  and  conclusions  for  all  Sacramento 
Valley  clay  soils  can  not  and  should  not  be  drawn  from  the  experience  reported 
herein  with  the  Tehama  clays  under  investigation  at  Willows. 


294  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

The  figures  given  should  make  it  very  plain  that  soils  into  which 
irrigation  water  percolates  with  difficulty  should  be  watched  very  care- 
fully at  depths  from  four  to  six  feet  below  the  surface.  The  ex- 
perience of  the  field  investigators  at  Willows  indicated  that  this  care 
is  especially  necessary  even  early  in  the  summer  in  order  to  insure 
that  an  adequate  irrigation  supply  shall  replace  the  moisture  absorbed 
from  the  winter  rainfall  after  that  has  been  utilized.11 


11  What  is  said  in  the  text  regarding  desirable  moisture  percentages  for 
Sacramento  Valley  soils  growing  alfalfa  considers  the  matter  only  from  the 
standpoint  of  the  total  annual  yields  of  hay.  It  is  obvious,  however,  that  the 
annual  yields  are  results  of  conditions  that  vary  from  day  to  day  and  from  week 
to  week.  For  instance,  considering  the  moisture  factor  only,  annual  differences 
in  yield  were  results  of  the  daily  and  weekly  differences  due  to  daily  and  weekly 
variations  in  soil  moisture.  The  data  collected  have  been  studied  with  reference 
to  the  effect  of  these  changing  moisture  percentages  on  the  seasonal  rates  of 
growth,  but  as  no  data  were  collected  to  indicate  daily  or  even  weekly  variations 
in  rates  of  growth,  making  it  necessary  to  rely  on  average  rates  of  growth 
between  cuttings,  such  deductions  as  were  suggested  in  the  study  have  not 
seemed  sufficiently  conclusive  to  warrant  their  presentation.  It  is,  however, 
possible  to  say  that  where  the  moisture  percentage  was  found  to  fall  below  the 
wilting  point  there  was  also  found  a  definite  falling  off  in  the  rate  of  alfalfa 
growth. 


